This invention relates to an engine starter motor and more particularly to an inertia sliding type starter motor in which the pinion slides along the shaft by inertia upon the rotation of the electric motor.
One example of the conventional inertia sliding type engine starter motor as shown in FIG. 6 is disclosed in Japanese Utility Model Laid-Open No. 56-107957. In FIG. 6, the engine starter motor comprises an over-running clutch 4 and a pinion 5 slidably mounted on the shaft 3 of an armature rotary shaft 2 extending from an electric motor 1. The over-running clutch 4 comprises a clutch outer member 4a having, teeth formed in the inner circumference of its boss which engage helical splines 6 formed in the shaft 3. The pinion 5 is formed integrally with a clutch inner member 4b and is slidably supported on the shaft 3 by a sleeve bearing 7 fitted on its inner circumferential surface. The armature rotary shaft 2 is supported by bearing 14 mounted to a front housing 15.
In FIG. 6, reference numeral 8 is an engine ring gear, 9 is a stopper secured to the end portion of the shaft 3, 10 is a return spring disposed between the stopper 9 and the pinion 5, and M is a power supply terminal for supplying electric power to the electric motor 1.
The operation of the conventional starter motor will now be described.
Referring to the circuit diagram shown in FIG. 7, when a key switch 11 of a vehicle is turned on, an electric current flows through a switch coil 13a of a solenoid switch 13 from a battery 12, causing a plunger 13b of the solenoid switch 13 to be repelled to bring a movable contact 13c into engagement with stationary contacts 13d and 13e, to thereby close the normally-open contacts. As a result, electrical power from the battery 12 is applied to the supply terminal M of the electric motor 1 and an electric current flows through a filed coil 1a and an armature coil 1b to cause the armature 1b to rotate. At this time, the over-running clutch 4 and the pinion 5 integral therewith slide forward (to the right in FIG. 6) because of the inclination of the helical splines 6 formed on the shaft 3 and the inertia of the over-running clutch 4 and the like against the return spring 10, whereby the pinion 5 meshes with the ring gear 8 to start the engine.
When the key switch 11 is turned off, the movable contact 13c separates from the stationary contacts 13d and 13e and returns to its original position due to a contact spring (not shown), whereby the power supply to the electric motor 1 is terminated and at the same time the pinion 5 together with the over-running clutch 4 is returned to the stationary position shown in FIG. 6 by compression force of the return spring 10.
The conventional engine starter motor of the above construction is disadvantageous in the following points:
(a) Since the pinion 5 is integrally formed with the clutch inner member 4b of the over-running clutch 4, the over-running clutch 4 also moves when the pinion 5 is moved to start the engine. Therefore, the mechanical impact exerted on the ring gear 8 from the pinion 5 during the initial stage of the meshing is large, so that the pinion 5 and/or the ring gear 8 can be damaged. PA1 (b) Since the distance between the pinion 5 and the bearing 14 mounted to the front housing 15 is long, the armature rotary shaft 2 has a cantilevered structure, and a large bending moment is generated at the armature rotary shaft which may cause its bending or destruction. PA1 (c) Since water splash may enter inside of the starter motor in the direction shown by an arrow in FIG. 6 because the pinion 5 and the sliding surfaces therefor are exposed, the shaft 3 may generate rust impeding smooth sliding movement of the pinion 5, and the return spring 10 may generate rust resulting in breakage. Also, the water which has entered through the gap between the clutch inner member 4a of the over-running clutch 4 and the front housing 15 may reach into the electric motor through the gap between the bearing 14 supporting the armature rotary shaft 2 and the armature rotary shaft 2, resulting in malfunctioning of the electric motor. This takes place particularly easily when, as in outboard engines or industrial engines, the crank shaft is in a vertical position, the flywheel is mounted in a horizontal position, and the starter motor is vertically installed with the pinion positioned at the top of it.